Central air conditioning (AC) systems typically rely on using utilitarian stamped metal fan blade designs for use with the outdoor air conditioning condenser in a very large and growing marketplace. In 1997 alone approximately five million central air conditioning units were sold in the United States, with each unit costing between approximately $2,000 to approximately $6,000 for a total cost of approximately $15,000,000,000(fifteen billion dollars). Conventional condenser fan blades typically have an air moving efficiency of approximately 25%. For conventional three-ton air conditioners, the outdoor fan power is typically 200–250 Watts which produces approximately 2000–3000 cfm of air flow at an approximately 0.1 inch water column (IWC) head pressure across the fan. The conventional fan system requires unnecessarily large amounts of power to achieve any substantial improvements in air flow and distribution efficiency. Other problems also exist with conventional condensers include noisy operation with the conventional fan blade designs that can disturb home owners and neighbors.
Air-cooled condensers, as commonly used in residential air conditioning systems, employ finned-tube construction to transfer heat from the refrigerant to the outdoor air. As hot, high pressure refrigerant passes through the coil, heat in the compressed refrigerant is transferred through the tubes to the attached fins. Electrically powered fans are then used to draw large quantities of outside air across the finned heat transfer surfaces to remove heat from the refrigerant so that it will be condensed and partially sub-cooled prior to its reaching the expansion valve.
Conventional AC condenser blades under the prior art are shown in FIGS. 1–3, which can include metal planar shaped blades 2, 4, 6 fastened by rivets, solder, welds, screws, and the like, to arms 3, 5, and 7 of a central condenser base portion 8, where the individual planar blades(4 for example) can be entirely angle oriented.
The outside air conditioner fan is one energy consuming component of a residential air conditioning system. The largest energy use of the air conditioner is the compressor. Intensive research efforts has examined improvements to it performance. However, little effort has examined potential improvements to the system fans. These include both the indoor unit fan and that of the outdoor condenser unit.
Heat transfer to the outdoors with conventional fans is adequate, but power requirements are unnecessarily high. An air conditioner outdoor fan draws a large quantity of air at a very low static pressure of approximately 0.05 to 0.15 inches of water column (IWC) through the condenser coil surfaces and fins. A typical 3-ton air conditioner with a seasonal energy efficiency ratio (SEER) of 10 Btu/W moves about 2500 cfm of air using about 250 Watts of motor power. The conventional outdoor fan and motors combination is a axial propeller type fan with a fan efficiency of approximately 20% to approximately 25% and a permanent split capacitor motor with a motor efficiency of approximately 50% to approximately 60%, where motor efficiency is the input energy which the motor converts to useful shaft torque, and where fan efficiency is the percentage of shaft torque which the fan converts to air movement.
In conventional systems, a ⅛ hp motor would be used for a three ton air conditioner (approximately 94 W of shaft power). The combined electrical air “pumping efficiency” is only approximately 10 to approximately 15%. Lower condenser fan electrical use is now available in higher efficiency AC units. Some of these now use electronically commutated motors (ECMs) and larger propellers. These have the capacity to improve the overall air moving efficiency, but by about 20% at high speed or less. Although more efficient ECM motors are available, these are quite expensive. For instance a standard ⅛ hp permanent split capacitor (PSC) condenser fan motor can cost approximately $25 wholesale whereas a similar more efficient ECM motor might cost approximately $135. Thus, from the above there exists the need for improvements to be made to the outdoor unit propeller design as well as for a reduction to the external static pressure resistance of the fan coil unit which can have large impacts on potential air moving efficiency.
Over the past several years, a number of studies have examined various aspects of air conditioner condenser performance, but little examining specific improvements to the outdoor fan unit. One study identified using larger condenser fans as potentially improving the air moving efficiency by a few percent. See J. Proctor, and D. Parker (2001). “Hidden Power Drains: Trends in Residential Heating and Cooling Fan Watt Power Demand,” Proceedings of the 2000 Summer Study on Energy Efficiency in Buildings, Vol. 1, p. 225, ACEEE, Washington, D.C. This study also identified the need to look into more efficient fan blade designs, although did not undertake that work. Thus, there is an identified need to examine improved fan blades for outdoor air conditioning units.
Currently, major air conditioner manufacturers are involved in efforts to eliminate every watt from conventional air conditioners in an attempt to increase cooling system efficiency in the most cost effective manner. The prime pieces of energy using equipment in air conditioners are the compressor and the indoor and outdoor fans.
Conventional fan blades used in most AC condensers are stamped metal blades which are cheap to manufacture, but are not optimized in terms of providing maximum air flow at minimum input motor power. Again, FIGS. 1–3 shows conventional stamped metal condenser fan blades that are typically used with typical outdoor air conditioner condensers such as a 3 ton condenser.
In operation, a typical 3-ton condenser fan from a major U.S. manufacturer draws approximately 195 Watts for a system that draws approximately 3,000 Watts overall at the ARI 95/80/67 test condition. Thus, potentially cutting the outdoor fan energy use by approximately 30% to 50% can improve air conditioner energy efficiency by approximately 2% to 3% and directly cut electric power use.
Residential air conditioners are a major energy using appliance in U.S. households. Moreover, the saturation of households using this equipment has dramatically changed over the last two decades. For instance, in 1978, approximately 56% of U.S. households had air conditioning as opposed to approximately 73% in 1997 (DOE/EIA, 1999). The efficiency of residential air conditioner has large impacts on utility summer peak demand.
Various information on typical air conditioner condenser systems can be found in references that include:    DOE/EIA, 1999. A Look at Residential Energy Consumption in 1997, Energy Information Administration, DOE/EIA-0632 (97), Washington, D.C.    Parker, D. S., J. R. Sherwin, R. A. Raustad and D. B. Shirey III. 1997, “Impact of Evaporator Coil Air Flow in Residential Air Conditioning Systems,” ASHRAE Transactions, Summer Meeting, Jun. 23–Jul. 2, 1997, Boston, Mass.    J. Proctor and D. Parker (2001). “Hidden Power Drains: Trends in Residential Heating and Cooling Fan Watt Power Demand,” Proceedings of the 2000 Summer Study on Energy Efficiency in Buildings, Vol. 1, p. 225, ACEEE, Washington, D.C.    J. Proctor, Z. Katsnelson, G. Peterson and A. Edminster, Investigation of Peak Electric Load Impacts of High SEER Residential HVAC Units, Pacific Gas and Electric Company, San Francisco, Calif., September, 1994.
Many patents have been proposed over the years for using fan blades but fail to deal with specific issues for making the air conditioner condenser fans more efficient for flow over the typical motor rotational speeds. See U.S. Pat. No.: 4,526,506 to Kroger et al.; U.S. Pat. No. 4,971,520 to Houten; U.S. Pat. No. 5,320,493 to Shih et al.; U.S. Pat. No. 6,129,528 to Bradbury et al.; and U.S. Pat. No. 5,624,234 to Neely et al.
Although the radial blades in Kroger '506 have an airfoil, they are backward curved blades mounted on an impeller, typically used with a centrifugal fan design typically to work against higher external static pressures. This is very different from the more conventional axial propeller design in the intended invention which operates against very low external static pressure (0.05–0.15 inches water column—IWC).
Referring to Houten '520, their axial fan describes twist and taper to the blades, and incorporates a plurality of blades attached to an impeller, rather than a standard hub based propeller design. This impeller is not optimal for standard outdoor air conditioning systems as it assumes its performance will be best when it is heavily loaded and is located very close to the heat exchanger (as noted in “Structure and Operation”, Section 50). In a standard residential outdoor air conditioner, the fan is located considerably above the heat exchange surfaces and the fan operates in a low-load condition under low external static pressure. This distinction is clear in FIG. 1 of the Houten apparatus where it is intended that the fan operate immediately in front of the heat exchange surface as with an automobile air conditioning condenser (see High Efficiency Fan, 1, last paragraph). The blades also do not feature a true air foil with a sharp trailing edge shown in FIG. 4A–4B.
Referring to Shih et al. '493, the axial fan describes features twisted blades, but are designed for lower air flow and a lower as would be necessary for quietly cooling of office automation systems. Such a design would not be appropriate for application for air condition condenser fan where much large volumes of air (e.g. 2500 cfm) must be moved at fan rotational velocities of 825–1100 rpm. The low air flow parameters and small air flow produced are clearly indicated in their “Detailed Description of the Invention.” The speed and air flow requirements for residential air conditioning condensers require a considerably different design for optimal air moving performance.
Referring to Bradbury '528, that device encompasses an axial fan designed to effectively cool electronic components in a quiet manner. The fans feature effective air foils, but the specific blade shape, chord, taper and twist are not optimized for the specific requirements for residential air conditioning condensers (825–1100 rpm with 2000–4800 cfm of air flow against low static pressures of 0.10–0.15 IWC) Thus, the cross sectional shapes and general design of this device are not relevant to the requirements for effective fans for air conditioner condensers. The limitations of Bradbury are clearly outlined in Section 7, 40 where the applicable flow rates are only 225 to 255 cfm and the rotational rates are 3200 to 3600 rpm. By contrast, the residential air conditioner condenser fans in the proposed invention can produce approximately 2500 to approximately 4500 cfm at rotational velocities of approximately 825 to approximately 1100 rpm
The Neely '234 patented device consists of an axial fan designed for vehicle engine cooling. Although its blades include a twisted design and airfoil mounted on a ring impeller, it does not feature other primary features which distinguished the proposed invention. These are a tapered propeller design optimized for an 825–1100 RPM fan speed and for moving large quantities of air (2000–2500 cfm) at low external static pressure. As with the prior art by Houten, the main use for this invention would be for radiator of other similar cooling with an immediately adjacent heat exchanger. The Neely device is optimized for higher rotational speeds (1900–2000 rpm) which would be too noisy for outdoor air conditioner condenser fan application (see Table 1). It also does not achieve sufficient flow as the Neely device produces a flow of 24.6–25.7 cubic meters per minute or 868 to 907 cfm—only half of the required flow for a typical residential air conditioner condenser (Table 1). Thus, the Neely device would not be use relevant for condenser fan designs which need optimization of the blade characteristics (taper, twist and airfoil) for the flow (approximately 2500 to approximately 4500 cfm) and rotational requirements of approximately 825 to approximately 1100 rpm.
The prior art air conditioning condenser systems and condenser blades do not consistently provide for saving energy at all times when the air conditioning system operates and do not provide dependable electric load reduction under peak conditions.
Thus, improved efficiency of air conditioning condenser systems would be both desirable for consumers as well as for electric utilities.